The present invention relates to a rear wheel suspension arrangement for motor vehicles.
A prior art rear wheel suspension arrangement is disclosed in U.S. Pat. No. 4,181,322, British Patent No. 1,545,393, West German Patent No. 2,645,272 and French Patent No. 2,366,947, all equivalent. The rear wheel suspension arrangement has, as shown in FIG. 1, longitudinal stay 01 (a front link arm) connected at one end side thereof with a vehicle body side and mounted at the other end side thereof at a wheel side, and lateral stay 02 (a rear link arm) rotatably mounted at one end side thereof at the rear position from stay 01 at the body side and at the other end side thereof at the wheel side. Stay 02 is formed, for example, of a resilient member such as a leaf spring. Rotatable bearing 012 is interposed between stay 01 and the body side, rotatably mounted at one end side thereof at the body side, and hingedly coupled between the other end side of bearing 012 and stay 01 through a pin for forming a vertical bearing axis. In this case, cylindrical sleeve 017 is formed at stay 01, and a bushing formed of a resilient material is interposed between sleeve 017 and bearing 012. Further, the bushing is provided with recesses which extend in the horizontal direction. Though not shown in the drawings, wheel support member 09, which itself is supported by stay 01, is further provided with another lateral stay which is arranged above stay 02 to be positioned between wheel support member 09 and the vehicle body. Wheel support member 09 is supported by the abovewritten another lateral stay at its upper portion and by stay 01 at its lower portion.
When a brake force Br is acted on a rear wheel, a reaction reverse to the traveling direction is acted on stay 01, bearing 012 is pressed by the reaction toward the inside at the pin for forming an axis of rotation as a center, and as bearing 012 rotates, a rear wheel is rotated in a toe-in direction through the longitudinal stay to compensate for the displacement of the toe-out direction acted on the rear wheel by the brake force. In this case, the toe of the rear wheel is varied in response to the deflection of stay 01 formed of a leaf spring, and stay 02 is disposed at its normal position in the state that the leaf spring is not deformed.
However, since the lateral stay is, for example, formed of a resilient member such as a leaf spring in the conventional rear wheel suspension arrangement, there arises a problem that the thickness of the leaf spring cannot be reduced in thickness due to the buckling strength of the lateral stay. Thus, since the thickness of the leaf spring of the lateral stay tends to increase, the leaf spring is hardly resiliently deformed. Such drawbacks exist that, when the leaf spring of stay 02 is elastically deformed, a relatively large force is necessary and merely a small amount of toe-in operation can be obtained. In other words, since the rear wheel does not exert the toe-in change if a relatively large brake force is not acted, a desired toe-in change cannot be obtained in case of cornering while lightly braking or while engine braking. In this case, there tends to be an oversteer condition, thereby resulting in loss of automotive traveling stability.
Further, since the conventional rear wheel suspension arrangement is provided with still another lateral stay, not shown, for supporting wheel support member 09 above stay 02, when stay 02, made of a leaf spring, is deformed, stay 01, for supporting member 09 below, displaces toward the inside of the vehicle body so that member 09 tilts in the outside of the body to cause a camber-variation, thereby resulting in a difficulty due to an increase in the camber angle with respect to the ground surface. Therefore, the vehicle is effected by a large lateral force when rapidly turning at a corner, so that, when stay 02 is deformed at the outer wheel side at the turning time, the increase in the camber angle with respect to the ground surface is aided, with the result that the ground contacting area of the wheel at the outer wheel side at the turning time which must produce larger ground contacting force decreases, thereby resulting in a difficulty due to a decrease in the cornering limit of the vehicle.
If the above-mentioned rear wheel suspension arrangement is not precisely balanced in the spring constants of stays 02, shapes and spring constants of bushings, and the shapes, sizes and dispositions of stays, the aforementioned difficulties cannot be suppressed to ranges so as not to lose the utility, and there arise drawbacks of a number of designing inconveniences as well as a complicated construction, necessity of accurate machining and an expensive cost.
In the conventional rear wheel suspension arrangement, the momentary central point O of the suspension disposed at the crossing point between the extension line of bearing 012 and the extension line of the lateral stay displaced forward at a distance l with respect to the axle of the rear wheel as shown in FIG. 1, when a lateral force F is applied to the rear wheel of outer wheel side toward the inside of the vehicle at the vehicle body turning time, the bushings of the suspension are resiliently deformed by the moment around the momentary central point O, so that the rear wheel displaces toward the toe-out direction with the result that there arises a drawback that the vehicle tends to be oversteered.